1. Field of the Invention
This invention relates to a method of manufacturing magnet material, a ribbon-shaped magnet material, magnetic powder and a bonded magnet.
2. Description of the Prior Art
Bonded magnets formed by binding magnetic powder with a binding resin are used for motors and various kinds of actuators because of the advantages that they have a wide versatility on their shapes.
A magnet material composing a bonded magnet is manufactured, for example, by a quenching method employing a melt spinning apparatus. When the melt spinning apparatus is equipped with a single cooling roll, the method is referred to as a single roll method.
In the single roll method, a magnet material with prescribed alloy composition is melted by heating, the molten metal is jetted from a nozzle, to be collided with the peripheral surface of the cooling roll rotating with respect to the nozzle, and solidified by quenching through contact with the peripheral surface to form in a continuous manner a ribbon-shaped magnet material, namely, a melt spun ribbon (quenched ribbon). The melt spun ribbon is milled into magnetic powder, and a bonded magnet is manufactured using the magnetic powder.
The cooling roll used in the single roll method is generally formed of a copper alloy, an iron alloy or the like. Moreover, for the purpose of improving the durability, a metallic or alloy surface layer, such as of chromium plating, may be provided on the peripheral surface of the cooling roll.
However, the peripheral surface of the cooling roll is usually formed of a metal having high heat conductivity, so that the difference in the microstructure (difference in the crystal grain diameter) between the roll contact surface (surface making contact with the peripheral surface of the cooling roll) and the free surface (surface opposite to the roll contact surface) of the obtained melt spun ribbon is large due to the difference in the cooling rate. Because of this, when magnetic powder is obtained by milling the ribbon, their magnetic properties are dispersed from one magnetic powder to another, and hence the bonded magnets manufactured by using these magnetic powders do not have satisfactory magnetic properties.
Accordingly, it is an object of the present invention to provide a method of manufacturing a magnet material, a ribbon-shaped magnet material, magnetic powder and a bonded magnet that make it possible to produce a magnet with excellent magnetic properties and high reliability.
In order to achieve the object, the present invention is directed to a method of manufacturing a ribbon-shaped magnet material. The ribbon-shaped magnet material is manufactured by discharging a molten metal of the magnet material from a nozzle while rotating a cooling roll having a surface layer composed of ceramics on its outer periphery to be collided with said surface layer of said cooling roll and solidified by cooling. This method is characterized in that the time during which the magnet material is in contact with said surface layer of said cooling roll is not less than 0.5 ms when the molten metal of said magnet material is discharged from directly above the center of rotation of said cooling roll toward an apex part of said cooling roll to be collided with the apex part.
According to the manufacturing method described above, it becomes possible to manufacture a magnet material having excellent magnetic properties and excellent heat resistance and corrosion resistance.
In the present invention, it is preferred that the thickness of said surface layer is in the range of 0.5 to 50 xcexcm. This makes it possible to reduce the difference in the crystal grain diameter between the contact surface side of the ribbon-shaped material which is in contact with the surface layer which is the peripheral surface of the cooling roll (roll contact surface side) and the opposite surface side of the ribbon-shaped material which is opposite to the roll contact surface side (the free surface side), thereby enabling to provide a magnet material especially having excellent magnetic properties.
Further, it is also preferred that the radius of said cooling roll is in the range of 50 to 500 mm. This makes it possible to provide a magnet material having high magnetic properties without enlarging the size of the spinning apparatus.
Furthermore, it is also preferred that said cooling roll is rotated at a peripheral velocity in the range of 5 to 60 m/s. This makes it possible to fine the grain diameter appropriately, thereby enabling to provide a magnet material having excellent magnetic properties.
Moreover, it is also preferred that the surface roughness Ra of said surface layer is in the range of 0.03 to 8 xcexcm. This makes it possible to improve contacting ability of the molten metal with respect to the surface layer of the cooling roll, thereby enabling to provide a magnetic material having excellent magnetic properties.
Moreover, it is also preferred that the thickness of the ribbon-shaped magnet material obtained is in the range of 10 to 50 xcexcm. The ribbon-shaped magnet material having the above thickness has less dispersion in its magnetic properties, so that it is possible to manufacture a magnet material having more excellent magnetic properties.
Moreover, it is also preferred that said magnet material is an alloy including rare-earth elements, transition metals and boron. This also makes it possible to provide a magnet material having excellent magnetic properties.
Another aspect of the present invention is directed to a ribbon-shaped magnet material. This ribbon-shaped material is manufactured by discharging a molten metal of the magnet material from a nozzle while rotating a cooling roll having a surface layer composed of ceramics on its outer periphery to be collided with said surface layer of said cooling roll and solidified by cooling, and the ribbon-shaped magnet material is characterized in that the time during which the magnet material is in contact with said surface layer of said cooling roll is not less than 0.5 ms when the molten metal of said magnet material is discharged from directly above the center of rotation of said cooling roll toward an apex part of said cooling roll to be collided with the apex part.
According to the invention as described above, it becomes possible to provide a ribbon-shaped magnet material from which a magnet having excellent magnetic properties and excellent heat resistance and corrosion resistance can be manufactured.
In this case, it is preferred that the thickness of said ribbon-shaped magnet material is in the range of 10 to 50 xcexcm. The ribbon-shaped magnet material having the above thickness has less dispersion in its magnetic properties, so that it is possible to manufacture a magnet material having more excellent magnetic properties.
It is also preferred that said magnet material is an alloy including rare-earth elements, transition metals and boron. This improves the magnetic properties further.
The other aspect of the present invention is directed to magnetic powder manufactured by milling a ribbon-shaped magnet material. The ribbon-shaped magnet material is obtained by discharging a molten metal of the magnet material from a nozzle while rotating a cooling roll having a surface layer composed of ceramics on its outer periphery to be collided with said surface layer of said cooling roll and solidified by cooling. The magnetic powder is characterized in that the time during which the magnet material is in contact with said surface layer of said cooling roll is not less than 0.5 ms when the molten metal of said magnet material is discharged from directly above the center of rotation of said cooling roll toward an apex part of said cooling roll to be collided with the apex part.
According to the invention as described above, it becomes possible to provide magnetic powder from which a magnet having excellent magnetic properties and excellent heat resistance and corrosion resistance can be manufactured.
In this case, it is preferred that said magnetic powder is an alloy including rare-earth elements, transition metals and boron. This improves the magnetic properties further.
Further, it is preferred that the magnetic powder was subjected to at least one heat treatment during its manufacturing process or after the manufacturing thereof. This makes it possible to homogenize the structure and remove the effect of stress introduced by the milling process, thereby enabling to further improve the magnetic properties.
Furthermore, it is also preferred that the said magnetic powder has a single phase structure or a nano-composite structure of which mean crystal grain diameter is equal to or less than 500 nm. This also improves the magnetic properties, in particular coercive force and rectangularity in the hysteresis curve.
Moreover, it is also preferred that the mean grain size of the magnetic powder is in the range of 0.5 to 150 xcexcm. This makes it possible to enhance the magnetic properties further.
Other aspect of the present invention is directed to a bonded magnet manufactured by bonding magnet powder with a binder, in which the magnet powder is obtained by milling a ribbon-shaped magnet material which is manufactured by discharging a molten metal of the magnet material from a nozzle while rotating a cooling roll having a surface layer composed of ceramics on its outer periphery to be collided with said surface layer of said cooling roll and solidified by cooling. The bonded magnet is characterized in that the time during which the magnet material is in contact with said surface layer of said cooling roll is not less than 0.5 ms when the molten metal of said magnet material is discharged from directly above the center of rotation of said cooling roll toward an apex part of said cooling roll to be collided with the apex part.
According to the invention as described above, it becomes possible to provide a bonded magnet having excellent magnetic properties and excellent heat resistance and corrosion resistance.
In this case, it is preferred that said magnetic powder is an alloy including rare-earth elements, transition metals and boron. This improves the magnetic properties further.
Further, it is also preferred that the content of the magnetic powder in the bonded magnet is in the range of 75 to 99.5 wt %. This makes it possible to possess high magnetic properties and high formability at manufacturing.
Furthermore, it is preferred that the coercive force Hcj of the bonded magnet is in the range of 320 to 900 kA/m. This makes it possible to perform excellent magnetization even when a sufficient magnetizing field can not be obtained, so that a sufficient magnetic flux can be obtained.
Moreover, it is also preferred that the maximum magnetic energy product (BH)max of the bonded magnet is equal to or greater than 60 kJ/m3. This makes it possible to obtain a magnet having high magnetic properties, and therefore if such a magnet is used for motors, high performance motors having high torque can be obtained.
The above described and other objects, structures and results of the present invention will be apparent when the following description of the preferred embodiment are considered taken in conjunction with the appended drawings.